Scan chain fault diagnosis
AssigneeTeseda Corporation
InventorsRich Ackerman, John Raykowski
Life of this patent
Estimating the term…
Abstract
Embodiments related to identifying a reference scan cell locationally related to a fault condition exhibited by a scan chain in which the reference scan cell is included are provided. A method for identifying a reference scan cell is provided, the method including, in a capture mode, outputting combinational logic values to scan cells in the scan chain so that scan cell values for the scan cells are based on respective combinational logic values, the combinational logic values electrically connected with the scan chain. The method further includes, in a shift mod, sequentially determining the scan cell value for each scan cell, and identifying as the reference scan cell a scan cell last determined to be at an expected logical state for that scan cell.
Claims19
At a failure analysis computing device, a method for identifying a reference scan cell locationally related to a fault condition exhibited by a scan chain in which the reference scan cell is included, the method comprising:
- in a capture mode, outputting combinational logic values to scan cells in the scan chain so that scan cell values for the scan cells are based on respective combinational logic values, the combinational logic values being generated by combinational logic cells electrically connected with the scan chain;
- in a shift mode:
- sequentially determining the scan cell value for each scan cell, and
- identifying as the reference scan cell a scan cell last determined to be at an expected logical state for that scan cell;
- identifying a particular scan cell providing output directly to the reference scan cell;
- and
- assigning a scan cell index to each scan cell according to a scan cell order, each scan cell being assigned a scan cell index that is different from the scan cell index of any other scan cell.
A failure analysis computing device for identifying a scan chain defect in a scan chain and a reference scan cell locationally related to the scan chain defect, the scan chain including a plurality of scan cells arranged according to a scan cell order, the failure analysis computing device comprising:
- a data-holding subsystem;
- and
- a logic subsystem for executing instructions stored in the data-holding subsystem to:
- in a detection mode:
- shift a test vector into the scan chain;
- without outputting combinational logic values to the scan cells from combinational logic cells electrically connected with the scan chain, sequentially determine a scan cell value for each scan cell;
- and
- identify a candidate scan chain defect condition based on the scan cell values so determined,
- in a capture mode, output combinational logic values to the scan cells so that scan cell values for the scan cells are based on respective combinational logic values, the combinational logic values being generated by the combinational logic cells, and
- in a shift mode:
- sequentially determine the scan cell value for each scan cell, and
- identify a reference scan cell last determined to be at an expected logical state for that scan cell.
At a failure analysis computing device, a method for determining an identity of a candidate reference scan cell locationally related to a fault condition exhibited by a scan chain in which the reference scan cell is included, the method comprising:
- in a first capture mode, outputting a first set of combinational logic values to scan cells in the scan chain so that a first set of scan cell values for the scan cells are based on respective elements of the first set of combinational logic values, the first set of combinational logic values being generated by combinational logic cells electrically connected with the scan chain;
- in a first shift mode:
- sequentially determining a first scan cell value for each scan cell, and
- identifying a first reference scan cell last determined to be at an expected logical state for that scan cell;
- identifying the first reference scan cell as the candidate reference scan cell;
- in a second capture mode, outputting a second set of combinational logic values to scan cells in the scan chain so that a second set of scan cell values for the scan cells are based on respective elements of the second set of combinational logic values;
- in a second shift mode:
- sequentially determining a second scan cell value for each scan cell, and
- identifying a second reference scan cell last determined to be at an expected logical state for that scan cell;
- and
- identifying the second reference scan cell as the candidate reference scan cell if the second reference scan cell is closer to a scan chain input for a scan cell order than the first reference scan cell.
Dependencies are inferred from the claim text.